Process for producing 2,3,5,6-tetrachloropyridine

ABSTRACT

In accordance with the present invention, 2,3,5,6-tetrachloropyridine is advantageously prepared by contacting pentachloropyridine in a solvent selected from the group consisting of alkylnitriles, water, alkylsulfoxides, tetramethylsulfone, C-1 to C-5 alcohols, alkyl carbonates and mixtures thereof, in the presence of an ammonium salt of an organic or inorganic acid with about 0.7 to about 1.1 g atoms of zinc per mole of pentachloropyridine.

This is a divisional of application Ser. No. 909,443 filed Sept. 19,1986 now U.S. Pat. No. 4,703,123.

BACKGROUND OF THE INVENTION

The present invention relates to an improved process for preparing2,3,5,6-tetrachloropyridine from pentachloropyridine(PCP).

2,3,5,6-Tetrachloropyridine is a valuable commercial product which canbe used for the production of insecticidal formulations. Furthermore,2,3,5,6-tetrachloropyridine is used as an intermediate for producingherbicidally effectiveα-[4-(3',5',6'-trichloropyrid-2'-yloxy)-phenoxy]-alkanecarboxylic acidsand derivatives thereof. The production and use of suchα-[4-(3',5',6'-trichloropyrid-2'-yloxy)-phenoxy]-alkanecarboxylic acidsand derivatives thereof are described, for example, in the U.S. Pat. No.4,133,675.

Methods are known for preparing 2,3,5,6-tetrachloropyridine frompentachloropyridine. U.S. Pat. No. 3,993,654 teaches a process ofpreparing tetrachloropyridine by reacting pentachloropyridine, zinc andhydrochloric acid in an aqueous medium at a temperature of at least 110°C. under at least autogeneous pressure. U.S. Pat. No. 4,259,495 teachesa process of preparing 2,3,5,6-tetrachloropyridine by reactingpentachloropyridine with zinc in an alkanephosphoric acid dialkyl estersolvent in the presence of an ammonium salt. Although achieving goodyields, this process has the serious disadvantage that it is difficultto separate the alkanephosphoric acid dialkyl ester solvent from thedesired 2,3,5,6-tetrachloropyridine product without elaborate orsophisticated separation apparatus. Another disadvantage is that thehigh boiling point of the alkanephosphoric acid dialkyl ester solventmakes this solvent difficult to recycle in industrial processes,requiring incineration or land disposal of an otherwise expensive andpolluting solvent. U.S. Pat. No. 4,259,495 also discloses that theprocess employs 1.2 to 1.6 gram-atoms of zinc per mole ofpentachloropyridine. Zinc is one of the most expensive reactants used inthe process of making 2,3,5,6-tetrachloropyridine frompentachloropyridine. It would clearly be desirable to carry out aprocess which utilizes a solvent which can be readily recycled and whichutilizes zinc even more efficiently than the process disclosed in U.S.Pat. No. 4,259,495 in order to reduce operating expenses involved withwaste disposal and the cost of zinc.

SUMMARY OF THE INVENTION

In accordance with the present invention, 2,3,5,6-tetrachloropyridine isadvantageously prepared by contacting pentachloropyridine in a solventselected from the group consisting f alkylnitriles, water,alkylsulfoxides, tetramethylsulfone, C-1 to C-5 alcohols, alkylcarbonates and mixtures thereof, in the presence of an ammonium salt ofan organic or inorganic acid with about 0.7 to about 1.1 g atoms of zincper mole of pentachloropyridine.

Preferably, the solvent employed is an alkylnitrile, alkylsulfoxide, ora mixture thereof with water. Most preferably, the alkylnitrile solventis acetonitrile and the alkylsulfoxide solvent is dimethylsulfoxide(DMSO). Preferably, the ammonium salt is ammonium chloride. Alsopreferred is that the process employs about 1.0 g atom of zinc per moleof pentachloropyridine.

The process of the present invention has the advantage of utilizingsolvents which are readily separated from the desired product and whichlend themselves to conventional recycling procedures. The presentprocess also has the unobvious advantage of utilizing zinc moreefficiently than disclosed in previously known methods.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The desired product 2,3,5,6-tetrachloropyridine is represented by theformula: ##STR1##

One of the requisite starting materials, pentachloropyridine, isrepresented by the formula: ##STR2##

Readily recyclable solvents suitable for contacting pentachloropyridinewith the requisite ammonium salt and zinc reactants should be thosesolvents which can readily be separated from the reaction mixture aftercompletion of the reaction. Representative solvents suitable for suchcontacting include but are not limited to alkylnitriles, water,alkylsulfoxides, tetramethylsulfone, C-1 to C-5 alcohols, alkylcarbonates and mixtures thereof.

Suitable alkylnitriles which can be used according to the invention assolvents are of the formula R-C.tbd.N, wherein R is C-1 to C-5 alkyl;the compound is acetonitrile wherein R is methyl.

Suitable alkylsulfoxides which can be used according to the invention assolvents are of the formula: ##STR3## wherein R independently representsC-1 to C-5 alkyl, more preferably C-1 to C-3 alkyl. Most preferably, Ris methyl, otherwise known as dimethylsulfoxide (DMSO).

Water, at least equivalent in quality to, that used for industrialpurposes, is a solvent which can be used according to the invention.

Tetramethylene sulfone, as a solvent which can be used according to theinvention, is represented by the formula: ##STR4##

C-1 to C-5 alcohols which can be used according to the invention assolvents include, but are not limited to, methanol, ethanol, n-proponal,t-propanol, n-butanol, iso-butanol and n-pentanol, preferablyiso-butanol.

Alkylcarbonates which can be used according to the invention as solventsare of the generic formula: ##STR5## wherein R independently representsC1-C5 alkyl. Representative alkylcarbonates include, but are not limitedto, dimethylcarbonate, methyl ethyl carbonate, diethyl carbonate, ethylpropyl carbonate and the like.

The process of the present invention can be conducted using theabove-mentioned solvents in about technical grade or better quality. Incertain instances, mixtures of the above solvents can be advantageouslyemployed. Preferred mixtures include acetonitrile and water; anddimethylsulfoxide and water.

The amount of solvent to be employed in the process of the presentinvention is expressed as a ratio of pentachloropyridine to solvent.Generally, the process is conducted using, on a weight percentage basis,a ratio of 1:2 to about 1:200 or more (pentachloropyridine:solvent),preferably in a range of about 1:4 to about 1:20. Most preferably, theprocess is conducted employing a saturated solution ofpentachloropyridine in the solvent, using sufficient solvent to justdissolve all the pentachloropyridine.

Within the temperature range of about 50° to about 175° C., in which theprocess according to the invention can be performed, temperatures ofabout 78° to about 120° C. are preferred.

The quarternary ammonium salts which can be used in the presentinvention contain, as the cation, the ammonium ion, or the stericallyfeasible derivatives derived therefrom by partial or completereplacement of the hydrogen atoms by alkyl and/or phenyl groups, whereinthe phenyl groups can be unsubstituted or substituted by 1 to 3 simplesubstituents such as alkyl, alkoxy or halogen. The ammonium salts usableaccording to the invention contain as anion the radical of any inorganicor organic acid capable of forming ammonium salts, such as a stronginorganic or organic acid with a pka of 2 or less.

Advantageously applicable ammonium salts correspond to the formula:##STR6## in which R₁, R₂, R₃ and R₄ are sterically feasible and can beidentical or different and are each hydrogen, alkyl having 1 to 4 carbonatoms, or phenyl or substituted phenyl which is substituted by up to 3halogens, or by alkyl groups having 1 to 4 carbon atoms or by alkoxygroups having 1 to 4 carbon atoms; X is an anion selected from thegroup: chloride, bromide, sulfate, hydrogen sulfate, phosphate, hydrogenphosphate, dihydrogen phosphate, acetate, propionate, butyrate,isobutyrate, oxalate, benzoate, benzenesulfonate and alkylsulfonateshaving 1 to 4 carbon atoms in the alkyl group; and n is 1 to 3 andcorresponds to the number of negative charges of the respective anion X.

The amount of ammonium salt to be employed in the current process is inthe weight ratio of about 1:1 to about 1:6,(pentachloropyridine:ammonium salt) preferably from about 1:2 to about1:4.

Pressures within which the process of the present invention can beconducted range suitably from atmospheric up to the autogenous vaporpressure of the solvent at its boiling point.

The zinc to be used according to the invention is finely divided in theform of zinc chips or granules or preferably in the form of zinc dust.

The amount of zinc can range from about 0.7 to about 1.1 gram atoms ofzinc per mole pentachloropyridine, preferably about 1.0 gram atoms ofzinc per mole of pentachloropyridine in order to obtain optimum zincutilization, while reacting most of the PCP.

The desired 2,3,5,6-tetrachloropyridine can be recovered from thereaction mixture by various procedures, depending in part on the type ofsolvent employed. Representative procedures include, but are not limitedto one or more of distillation, extraction, phase separation,crystallization and filtration, preferably distillation and filtrationwhere acetonitrile is employed as the solvent.

The following examples are presented to illustrate typical processes ofthe present invention, but the scope of the invention is not to beconsidered limited to the specific examples given.

EXAMPLE 1--ACETONITRILE SOLVENT AND AMMONIUM CHLORIDE

To a flask are added 35 grams (g) (0.139 mole (mol)) ofpentachloropyridine (PCP) and 199 g of acetonitrile. The mixture isstirred vigorously and heated to reflux 978 degrees Centigrade (° C.))to dissolve the PCP. To the reactive mixture is added 9.61 g (0.139 mol)of 93.7 percent pure metallic zinc dust, (g atom zinc:molepentachloropyridine ratio is 1:1). A solution of 15.08 g (0.282 mol)ammonium chloride (NH₄ Cl) in 40.2 g water is added drop-wise over a 45minute (min) period. After agitation for another 2.25 hours (hr), 17.74g of 12 normal (N) hydrochloric acid is added, a distillation head isattached to the reaction flask, and 164 g of material is distilled outat an overhead temperature of 77-78° C. To the pot is added 137.5 g of6.25N hydrochloric acid and the mixture is stirred for 1 hr. Thechloropyridines precipitate out of solution as a white solid and areremoved by vacuum filtration prior to drying to a constant weight in avacuum oven. Analysis of the chloropyridines by gas chromatography givesa molar selectivity of the pentachloropyridine converted of:

99.35 percent (%) desired product, viz., 2,3,5,6-tetrachloropyridine(28.977 g)

0.22% to 2,3,5-trichloropyridine (0.054 g),

0.01% to 2,3,4,5-tetrachloropyridine (0.003 g), and

0.42% to 2,3,4,6-tetrachloropyridine (0.122 g),

at 96.75 percent pentachloropyridine conversion. Of the metallic zincused in the reaction. 95.61 percent reacts with chloropyridine with91.71 percent resulting in the formation of 2,3,5,6-tetrachloropyridine.Of the metallic zinc added, 100 percent oxidizes during the reactionwith 99.16 percent of it accounted for in the final products.

EXAMPLE 2--ACETONITRILE SOLVENT AND AMMONIUM ACETATE

To a flask are added 35 g (0.139 mol) of pentachloropyridine, 21.5 g(0.28 mol) ammonium acetate, 40 g water, and 200 g acetonitrile and thecompounds are heated to reflux (78° C.) while being agitated vigorously.Subsequently, 9.75 g (0.140 mol) of 93.7 percent zinc dust, (g atomzinc: moles pentachloropyridine is 1:1), is added and the solution isrefluxed for 3.58 hrs. After the reaction is complete, a distillationhead is attached and 188 g of material is removed overhead. Water andperchloroethylene are added to the flask, partitioning the organic(341.2 g) and aqueous (336.2 g) phases. Analysis for chloropyridines inthe organic phase by gas chromatography and for zinc in the aqueousphase by wet methods indicates a molar selectivity of thepentachloropyridine converted of:

96.90% to 2,3,5,6-tetrachloropyridine (27.899 g)

0.19% to 3,5-dichloropyridine (0.037 g),

0.46% to 2,3,5-trichloropyridine (0.111 g),

0.15% to 2,3,6-trichloropyridine (0.36 g),

0.07% to 2,3,4,5-tetrachloropyridine (0.020 g),

2.23% to 2,3,4,6-tetrachloropyridine (0.642 g), and

at 95.07 percent pentachloropyridine conversion with 98.13 percent ofthe pentachloropyridine added accounted for in the final products. Ofthe metallic zinc used in the reaction, 95.61 percent reacts withchloropyridines with 91.72 percent resulting in the formation of2,3,5,6tetrachloropyridine. Of the metallic zinc added, 100 percentoxidizes during the reaction.

EXAMPLE 3--WATER SOLVENT AND AMMONIUM CHLORIDE

A flask containing 115 g (0.458 mol) of pentachloropyridine, 31.61 g(0.453 mol) of 93.7 percent metallic zinc dust, (g atom zinc:molespentachloropyridine is 1:1), 49 g (0.906 mol) ammonium chloride, and 125g water is heated to reflux (100° C.) for 6.0 hrs while being agitatedvigorously. The reaction mixture is quenched by adding 250 g of tolueneand 280 g of water. Any solids remaining in the reaction mixture arefiltered out (0.03 g) of the solution prior to the addition of 15 g of12N hydrochloric acid, partitioning the aqueous and organic phases.Analysis for chloropyridines in the organic phase by gas chromatographyand analysis for zinc in the aqueous phase by wet methods indicates amolar selectivity of the pentachloropyridine converted of:

96.88% to 2,3,5,6-tetrachloropyridine (90.073 g)

0.12% to 3,5-dichloropyridine (0.076 g),

0.96% to 2,3,5-trichloropyridine (0.751 g),

0.23% to 2,3,6-trichloropyridine (0.180g),

0.06% to 2,3,4,5-tetrachloropyridine (0.056 g),

1.75% to 2,3,4,6-tetrachloropyridine (1.627 g), and

at a 93.60 percent pentachloropyridine conversion with 97.12 percent ofthe pentachloropyridine added accounted for in the final product. Of themetallic zinc used in the reaction, 95.76 percent reacts withchloropyridine with 91.47 percent resulting in the formation of2,3,5,6-tetrachloropyridine. Of the metallic zinc added, 100 percentoxidizes during the reaction with 99.16 percent of it accounted for inthe final reaction products.

EXAMPLE 4--DIMETHYLSULFOXIDE SOLVENT AND AMMONIUM CHLORIDE

A flask containing 35.01 g (0.139 mol) of pentachloropyridine dissolvedin 220 g dimethylsulfoxide is heated to 100° C. To the flask is added9.62 g (0.139 mol) of 93.7 percent metallic zinc dust, (g atoms zinc:moles pentachloropyridine is 1:1). A solution of 9.73 g (0.182 mol)ammonium chloride in 29.6 g of water is added drop-wise with vigorousagitation over a 40 min period. The reaction mixture is maintained at100° C. for an additional 1.75 hr, filtered to remove any solids (0.2 g)and the chloropyridines are precipitated in the reaction mixture byadding 360 g water and 300 g of 6N hydrochloric acid. Thechloropyridines are filtered out of solution and dried in a vacuum ovento constant weight (30.0 g). Analysis of the chloropyridines by gaschromatography indicates a molar selectivity of the pentachloropyridineconverted of:

94.6% to 2,3,5,6-tetrachloropyridine (27.585 g)

0.29% to 2,3,5-trichloropyridine (0.071 g),

3.29% 2,3,4,5-tetrachloropyridine (0.956 g), and

1.46% 2,3,4,6-tetrachloropyridine (0.424 g),

at 96.18 percent pentachloropyridine conversion with 99.6 percent of thepentachloropyridine added accounted for in the final product. Of themetallic zinc used in the reaction 97.37 percent reacts withchloropyridine with 92.20 percent resulting in the formation of2,3,5,6-tetrachloropyridine. Of the metallic zinc added, 100 percent,oxidizes and 98.90 percent is accounted for in the final product.

EXAMPLE 5--ISOBUTANOL SOLVENT AND AMMONIUM CHLORIDE

A flask containing 40.0 g (0.159 mol) of pentachloropyridine, 11.03 g90.159 mol) of 93.7 percent metallic zinc dust (g atom zinc:molespentachloropyridine is 1:1) and 135 g isobutanol is heated to reflux(92° C.) and the reactants are vigorously agitated. A solution of 17.03g (0.32 mol) ammonium chloride in 48.67 g water is added drop-wise tothe reaction mixture over 30 min. period. The reaction mixture isrefluxed for 4.42 hrs, then quenched with 170 g toluene and 227 g water.Any solids present are filtered out, and the organic phase is separatedfrom the aqueous phase. Analysis of the organic phase by gaschromatography indicates a molar selectivity of the pentachloropyridineconverted of:

91.02% to 2,3,5,6-tetrachloropyridine (31.418 g)

0.19% to 3-chloropyridine (0.34 g),

0.54% to 3,5-dichloropyridine (0.127 g),

5.13% to 2,3,5-trichloropyridine (1.490 g),

0.26% to 2,3,6-trichloropyridine (0.075 g),

0.33% to 2,3,4,5-tetrachloropyridine (0.114 g), and

2.54% to 2,3,4,6-tetrachloropyridine (0.877 g),

at 92.21 percent pentachloropyridine conversion with 98.94 percent ofthe pentachloropyridine added accounted for in the final product. Of themetallic zinc used in the reaction, 99.45 percent reacts withchloropyridine with 84.57 percent resulting in the formation of2,3,5,6-tetrachloropyridine. Of the metallic zinc added, 99.83 percentoxidizes and 96.03 percent is accounted for in final reaction products.

EXAMPLE 6--TETRAMETHYLENE SULFONE AND AMMONIUM CHLORIDE

A flask containing 35.01 g (0.139 mol) of pentachloropyridine, 9.62 g(0.139 mol) of 93.7 percent metallic zinc dust, (g atoms zinc:molespentachloropyridine is 1:1), and 249.1 g of tetramethylene sulfone(sulfolane) is heated to90° C. and the reactants are vigorouslyagitated. A solution of 9.68 g (0.181 mol) ammonium chloride in 29.2 gwater is added over a period of 35 min and the temperature of thereaction mixture is maintained at 90° C. for an additional 65 min. Anyinsoluble material is removed from the heated reaction mixture byfiltration (0.74 g) (at 76.9 percent Zn and 53.9 percent metallic Zn).The reaction mixture is quenched with 694 g water and 7 g 12Nhydrochloric acid, agitated for 1 hour (hr), the precipitatedchloropyridines are removed by vacuum filtration and dried in a vacuumoven. Analysis of the chloropyridines by gas chromatography indicates amolar selectivity of the pentachloropyridine converted of:

89.23% to 2,3,5,6-tetrachloropyridine (23.911 g)

5.18% to 2,3,5-trichloropyridine (1.168 g),

0.99% to 2,3,6-trichloropyridine (0.223 g),

0.32% to 2,3,4,5-tetrachloropyridine (0.086 g), and

4.27% to 2,3,4,6-tetrachloropyridine (1.144 g),

at 88.70 percent pentachloropyridine conversion with 96.10 percent ofthe pentachloropyridine added accounted for in the final product. Of themetallic zinc oxidized 99.47 percent reacted with chloropyridine with83.59 percent resulting in the formation of 2,3,5,6-tetrachloropyridine.Of the metallic zinc added, 85.59 percent oxidizes with 96.03 percentbeing accounted for in the final products.

EXAMPLE 7--ACETONITRILE SOLVENT AND AMMONIUM CHLORIDE

AT REDUCED ZINC:PENTACHLOROPYRIDINE

A flask containing 35.2 g (0.140 mol) of pentachloropyridine, 15.0 g(0.28 mol) ammonium chloride, 56.5 g water, and 201.3 g acetonitrile isheated to reflux (78° C.) and the reactants are agitated vigorously. Tothe reaction mixture is added 7.26 g (0.104 mol) of 93.7 percentmetallic zinc dust, (g atom zinc:moles pentachloropyridine is 0.74:1)and the reaction mixture is refluxed for 4.40 hrs. The heated reactionmixture is filtered to remove solids (0.17 g of material is recovered,whose analysis indicated 75.0 percent zinc). A distillation head isattached to the reaction flask and 222.1 g of material is removedoverhead. Water and toluene are added to the flask and the organic andaqueous phases are separated. Analysis of chloropyridines in the organicphase by gas chromatography and for zinc in the aqueous phase by wetmethods indicated a molar selectivity of the pentachloropyridineconverted of:

97.27% to 2,3,5,6-tetrachloropyridine (20.868 g)

0.05% to 3,5-dichloropyridine (0.007 g),

0.33% to 2,3,5-trichloropyridine (0.060 g),

0.04% to 2,3,6-trichloropyridine (0.007 g),

0.05% to 2,3,4,5-tetrachloropyridine (0.011 g), and

2.25% to 2,3,4,6-tetrachloropyridine (0.483 g),

at 70.63 percent pentachloropyridine conversation with 98.23 percent ofthe pentachloropyridine added accounted for in the final product. Of themetallic zinc, used in the reaction, 97.41 percent reacts withchloropyridine with 94.30 percent resulting in the formation of2,3,5,6-tetrachloropyridine. Of the metallic zinc added, 98.10 percentoxidizes with 99.37 percent being accounted for in the final products.

EXAMPLE 8--ACETONITRILE SOLVENT AND AMMONIUM CHLORIDE

AT REACTION TEMPERATURE OF 60° C.

To a reactor is added 35.0 g (0.139 mol) of pentachloropyridine, 9.62 g(0.139 mol) of 93.7 percent metallic zinc dust (g atom zinc:molespentachloropyridine is 1:1), 14.9 g (0.278 mol) ammonium chloride, 41.7g water and 202 g acetonitrile. The reactants are agitated, heated andmaintained at a temperature of 60° C. for 7.0 hrs. Analysis forchloropyridines by gas chromatography and for zinc by wet methodsindicated a molar selectivity of the pentachloropyridine converted of:

99.68% to tetrachloropyridines (30.106 g), and

0.32% to 2,3,5-trichloropyridine (0.081 g),

at a pentachloropyridine conversion of 73.4 percent.

EXAMPLE 9--ACETONITRILE SOLVENT AND AMMONIUM CHLORIDE AT A REACTIONTEMPERATURE OF 145° C.

To a two liter Parr reactor is added 190.09 g (0.760 mol) ofpentachloropyridine, 80.97 g (1.52 mol) ammonium chloride, 260 g water,52.89 g (0.760 mol) of 93.7 percent metallic zinc dust, (g atomzinc:moles pentachloropyridine is 1:1) and 814 g acetonitrile. Thereactor is sealed, the reactants agitated, the temperature of thereaction mixture is raised to 145° C. within 24 min, and maintained atthat temperature for 64 min. The reactor is allowed to cool to roomtemperature, the contents are transferred to a flask equipped with adistillation apparatus and 964 g of material are removed overhead. Then500 g toluene is added to the flask and the organic and aqueous layersthat form are separated. Analysis of the aqueous phase for zinc by wetmethods, and analysis of the organic phase for chloropyridines by gaschromatography indicates a molar selectivity of the pentachloropyridineconverted of:

88.67% to 2,3,5,6-tetrachloropyridine (130.541 g))),

1.34% to 3,5-dichloropyridine (1.346 g),

0.01% to 2,4,6-trichloropyridine (0.012 g),

3.20% to 2,3,5-trichloropyridine (3.963 g),

1.23% to 2,3,6-trichloropyridine (1.523 g),

0.11% to 2,3,4,5-tetrachloropyridine (0.162 g),

2.31% to 2,3,4,6-tetrachloropyridine (3.401 g),

0.05% to 2-aminotetrachloropyridine (0.079 g), and

3.08 percent 4-aminotetrachloropyridine (4.848 g) at 89.75 percentpentachloropyridine conversion with 95.90 percent of thepentachloropyridine added accounted for in the final product. Of themetallic zinc oxidized, 93.04 percent reacted with chloropyridine with79.34 percent resulting in the formation of 2,3,5,6-tetrachloropyridine.Of the metallic zinc added, 100 percent is oxidized in the course of thereaction with 93.4 percent accounted for in the final products.

Upon repeating Examples 1-9 utilizing any of the suitable ammonium saltsand solvent cited hereinbefore in place of those utilized in theExamples, substantially the same excellent results are obtainedregarding formation of the desired 2,3,5,6-tetrachloropyridine.

What is claimed is:
 1. A process for preparing2,3,5,6--tetrachloropyridine, comprising contacting pentachloropyridinein water and in the presence of a quaternary ammonium salt with about0.7 to about 1.1 gram atoms of zinc per mole pentachloropyridine.
 2. Theprocess of claim 14 wherein a solvent selected from the group consistingof C-1 to C-5 alkylnitrile, C-1 to C-5 alkylsulfoxide, tetramethylenesulfone, a C-1 to C-5 alcohol, a C-1 to C-5 alkylcarbonate or a mixturethereof is employed in combination with the water.
 3. The process ofclaim 14, wherein the ammonium salt is of an inorganic acid.
 4. Theprocess of claim 14 wherein the ammonium salt is ammonium chloride 5.The process of claim 14 conducted using between about 0.9 to about 1.1gram atoms of zinc per mole of pentachloropyridine.
 6. The process ofclaim 14, conducted using about 1.0 g atoms of zinc per mole ofpentachloropyridine.
 7. The process of claim 14 wherein the ammoniumsalt is ammonium chloride and the process is conducted using betweenabout 0.9 to about 1.1 g atoms of zinc per mole of pentachloropyridine.